1. Field of the Invention
The present invention relates to a data reproduction device and a reproduction method.
2. Description of the Related Art
Thanks to the recent development of digital audio recording technology, it is popular to record voice in an MD using an MD recorder instead of the conventional tape recorder. Furthermore, movies, etc., begins to be publicly distributed by using a DVD, etc., instead of the conventional videotape. Although a variety of technologies are used for such a digital audio recording technology and video recording technology, MPEG is one of the most popular technologies.
FIGS. 1 and 2 show the format of MPEG audio data.
As shown in FIG. 1, the MPEG audio data are composed of frames called AAU (Audio Access Unit or Audio Frame). The frame also has a hierarchical structure composed of a header, an error check, audio data and ancillary data. Here, the audio data are compressed.
The header is composed of information about a syncword, a layer and a bit rate, information about a sampling frequency, data, such as a padding bit, etc. This structure are common to layers I, II and III. However, the compression performances are different.
The audio data in the frame are composed as shown in FIG. 2. As shown in FIG. 2, the audio data always include a scale factor, regardless of layers I, II and III. This scale factor is data for indicating a reproduction scale factor of a wave. Specifically, since audio data indicated by the sampling data of layers I and II or the Huffman code bit of layer III are normalized by the scale factor, actual audio data can be obtained by multiplying the sampling data or data that are obtained by expanding the Huffman code bit, by the scale factor. The scale factor is further divided and compressed into 32 sections (sub-bands) along a time axis, and in the case of monaural sound, at maximum 32 scale factors are allocated.
For the details of the MPEG audio data, refer to ISO/IEC 11172-2, which is the international standard.
FIG. 3 shows the basic configuration of the conventional MPEG audio reproduction device.
If MPEG audio data are inputted to an MPEG audio input unit 10, the data are decoded in an MPEG audio decoding unit 11 for implementing processes specified in the international standard, and voice is outputted from an audio output unit 12 composed of a speaker, etc.
If digitally recorded voice is reproduced, a reproduce speed is frequently changed. Therefore, in particular, the speech speed conversion function is useful for both content understanding and content compression. However, if the speech speed of MPEG audio data is directly converted, conventionally the speech speed was converted after the data were decoded.
MPEG audio data can be compressed into one several tenth. Therefore, if the speech speed is converted after MPEG audio data are decoded, enormous data must be processed after the compressed data are expanded. Therefore, the number and scale of circuits required to convert a speech speed become large.
As a publicly known technology for converting a speech speed after decoding MPEG audio data, there is Japanese Patent Laid-open No. 9-73299.